Chemical Engineering Journal 173 (2011) 627– 635
Contents lists available at ScienceDirect
Chemical Engineering Journal
j ourna l ho mepage: www.elsev ier .c
Kinetic aly
blacks
Yuki Kam
a Heat and Flui 35–85
b Department o kayam
a r t i c l
Article history:
Received 4 Jun
Received in re
Accepted 4 Au
Keywords:
Methane catalytic decomposition
Carbon black
Kinetic study
Carbon deposition
Activation energy
Raman spectro
hibit c
activa
carbo
pectr
black
into account the effect of carbon deposition, and the significant difference between them was observed.
Then, the amount of deposited carbon was introduced in a kinetic study to represent the degree of change
in catalyst properties due to carbon deposition. On the basis of the observation that the time-varying cat-
alytic characteristics had clear correlations with the amount of deposited carbon, the evaluation method
of the activation energy in which the effect of carbon deposition is taken into account was presented.
1. Introdu
Decomp
because it c
ural gas [1,2
CH4 → C(s)
where H d
application
in which en
energy at h
thermal de
atures, whi
durability o
a catalytic p
∗ Correspon
1, Shin-nakaha
fax: +81 45 75
E-mail add
1385-8947/$ –
doi:10.1016/j.scopy The constant activation energy for each carbon black was obtained in the wide range of the amount of
deposited carbon. The presented method was demonstrated to be useful in determining activation ener-
gies of carbon blacks which exhibit the time-varying catalytic characteristics. Finally, Raman spectroscopy
was applied to carbon blacks, which included fresh ones and those used in the methane decomposition
experiment for specified reaction times. The obtained Raman spectra exhibited significant changes in the
initial deactivation stage. It was demonstrated that Raman spectroscopy was useful to characterize the
initial structural evolution of carbon blacks.
© 2011 Elsevier B.V. All rights reserved.
ction
osition of methane is an important chemical reaction
an be utilized to produce COx-free hydrogen from nat-
]. The overall reaction can be described as follows:
+ 2H2, H = 75 kJ/mol (1)
enotes the standard reaction enthalpy. One promising
of this reaction is the solar thermochemical process,
dothermic reactions are driven by concentrated solar
igh temperatures [3–9]. However, the non-catalytic
composition process requires high operating temper-
ch cause excessive heat loss and reduce the thermal
f the reactor materials. Therefore, it is useful to develop
rocess to lower the operating temperatures.
ding author at: Heat and Fluid Dynamics Department, IHI Corporation,
ra-cho, Isogo-ku, Yokohama 235–8501, Japan. Tel.: +81 45 759 2869;
9 2210.
ress: yuki.kameya.jp@gmail.com (Y. Kameya).
Carbonaceous materials exhibit catalytic activity in the decom-
position of methane and other hydrocarbons [10–26]. They offer
several advantages over metal catalysts: high temperature resis-
tance, tolerance to sulfur and other potentially harmful impurities
in the feedstock [12], and cost effectiveness [22]. The catalytic
characteristics of various carbon materials, such as graphite, dia-
mond, activated carbons, carbon blacks, glassy carbons, carbon
fibers, carbon nanotubes, and fullerenes, have been investigated
[10,12]. Among them, carbon blacks are promising because they
show reasonably high activities and long lifetimes, while other
carbonaceous materials exhibit low activities or rapid deactiva-
tion [10,12,14,18]. These catalytic characteristics of carbon blacks
are attributed to their microstructure which has many active
sites consisted of edges and defects in nanosized graphitic lay-
ers [14–18]. In catalytic decomposition of methane, the produced
carbon deposits on the surface active sites of carbon blacks
[18]. They show long lifetimes because deposited carbons also
exhibit catalytic activities, although carbon deposition causes the
change of the initial surface properties as methane decomposition
proceeds [24].
It is well known that carbon blacks exhibit time-varying cat-
alytic characteristics [10,14,18,22]. They deactivate from the start
see front matter © 2011 Elsevier B.V. All rights reserved.
cej.2011.08.017 and Raman spectroscopic study on cat
in methane decomposition
eyaa,b,∗, Katsunori Hanamurab
d Dynamics Department, IHI Corporation, 1, Shin-nakahara-cho, Isogo-ku, Yokohama 2
f Mechanical and Control Engineering, Tokyo Institute of Technology, 2-12-1-I1-25, Oo
e i n f o
e 2011
vised form 1 August 2011
gust 2011
a b s t r a c t
Carbon blacks have been known to ex
remain problems in determining the
the present study, the significance of
gated, and the applicability of Raman s
First, the activation energy of carbonom/ locate /ce j
tic characteristics of carbon
01, Japan
a, Meguro-ku, Tokyo 152–8552, Japan
atalytic activities in methane decomposition. However, there
tion energy and the time-varying catalytic characteristics. In
n deposition on carbon black in a kinetic study was investi-
oscopy to the characterization of carbon blacks was examined.
was determined at two temperature ranges without taking

628 Y. Kameya, K. Hanamura / Chemical Engineering Journal 173 (2011) 627– 635
of the reaction, and although the deactivation gradually becomes
moderate from the initial state, it continues and a steady state
is not reac
gravimetric
further tim
the activity
time-varyin
reaction ki
that signific
cal carbon
the differen
obtained fr
pared with
study of t
is importan
energies fo
characterist
The tex
carbon blac
ferences in
blacks and
several cha
blacks: nitr
evaluation [
for surface
crystallinity
in graphitic
transmissio
of the stru
surface are
investigated
has been r
tion, Lázaro
as the reac
ture of carb
ordered on
graphitic s
tion is inte
on the rea
that of car
well descri
terized ma
demonstrat
disordered
promising
evolution o
process.
In the p
on carbon
of methane
spectroscop
ined. First,
into accoun
that the ch
deposition
nite. Next,
carbon bla
degree of
sition. The
variation of
thermore,
which the
presented.
spectra of c
cess was in
discussed.
Table 1
Sample properties.
name SB285 SB905
ter (nm) 26 15
e area (m2/g) 81 212
erimental
rbon black samples
bon blacks essentially consist of elemental carbon and
tained by partial combustion or thermal decomposition of
arbons [32]. The primary particles in carbon blacks are
articles and they usually exist in the form of aggregates.
ave been used as an important material in various indus-
plications, such as rubber reinforcing and black pigments.
arious kinds of carbon blacks are commercially available.
carbon blacks were used in this study because they have
comparatively stable activities [18]. Two types of color car-
cks, SB285 and SB905 (Asahi Carbon, Japan), were employed.
lists
rer.
ethan
hem
posit
out
c tub
ere
26 m
hen
dilut
flow
e wi
aving
acto
of t
atio
PID
d in
mat
posit
ctor
blac
the i
Fig. 1. Schematic diagram of experimental setup.hed. In addition, it was indicated from the thermo-
analysis that some types of carbon black exhibit
e-varying characteristics: after the initial deactivation
increases and then deactivates again [22]. Theses
g catalytic behaviors make the determination of the
netic parameters indefinite. Lee et al. pointed out
ant difference in the activation energy of the identi-
black, Black Pearls 2000 (Cabot, US), was caused by
ce in the data employed for the analysis: 143 kJ/mol
om the data after 20–60 min of time on-stream, com-
238 kJ/mol at the initial near-zero time [18]. A detailed
his issue has not yet been reported. Therefore, it
t to establish an evaluation method of activation
r carbon blacks which exhibit time-varying catalytic
ics.
tural, surface-chemical, and structural properties of
ks have been investigated to help understand the dif-
catalytic activities between various types of carbon
the deactivation mechanism in their lifetimes. To date,
racterization techniques have been applied to carbon
ogen adsorption has been used for specific surface-area
12,14,16,18,24], temperature-programmed desorption
functional groups [24], X-ray diffraction (XRD) for
[24], X-ray photoelectron spectroscopy for defects
layers [26], and scanning electron microscopy and
n electron microscopy (TEM) for direct observation
cture [14,18]. In particular, the effect of specific
a on the catalytic characteristics has been widely
and a positive correlation with catalytic activity
eported [16]. With regard to structural characteriza-
et al. investigated the change in the XRD profiles
tion progressed, and demonstrated that the struc-
on black evolved from a highly disordered to a more
e because carbon deposited from methane has a more
tructure than the fresh catalyst [24]. This observa-
resting because it appears to be relevant to studies
ctivity of soot, whose microstructure is similar to
bon blacks. The oxidation behavior of soot has been
bed in connection with its microstructure, charac-
inly by using Raman spectroscopy, which has been
ed to be sensitive to nanostructural changes of highly
carbons [27–31], and TEM [28,30,31]. Therefore, it is
to use Raman spectroscopy to evaluate the structural
f carbon blacks during the methane decomposition
resent work, the significance of carbon deposition
black in a kinetic study of catalytic decomposition
was investigated, and the applicability of Raman
y to the characterization of carbon blacks was exam-
activation energies were evaluated without taking
t the effect of carbon deposition in order to show
ange in properties of carbon black caused by carbon
makes determination of activation energies indefi-
the mass ratio of deposited carbon to the initial
ck was introduced as a parameter representing the
change in catalyst properties due to carbon depo-
n, the influence of carbon deposition on the time
the methane decomposition rate was examined. Fur-
the evaluation method of the activation energy in
effect of carbon deposition is taken into account was
Finally, the change in spectral parameters of Raman
arbon blacks during the methane decomposition pro-
vestigated, and the applicability of the analysis was
Trade
Diame
Surfac
2. Exp
2.1. Ca
Car
are ob
hydroc
nanop
They h
trial ap
Thus, v
Color
shown
bon bla
Table 1
ufactu
2.2. M
A sc
decom
carried
electri
tubes w
ters of
used w
argon
a high
the tub
nace h
tube re
surface
bed loc
AMF-S
inserte
sheath
decom
the rea
carbon
under the specifications of the samples provided by the man-
e decomposition experiment
atic diagram of the experimental setup for the methane
ion experiment is shown in Fig. 1. The reaction test was
in a vertical quartz tube reactor heated by an ARF-30KC
e furnace (Asahi rika, Japan). Two types of the quartz
used: both having a height of 700 mm and inner diame-
m and 7 mm. The tube with 26 mm inner diameter was
the total gas flow rate was relatively high because of
ion. This is because the packed bed of carbon black had
resistance that caused the reactor pressure to rise when
th 7 mm inner diameter was used. The electric tube fur-
a height of 300 mm covered the central region of the
r. A K-type sheathed thermocouple was set on the outer
he quartz tube at the height of the carbon black-packed
n. The input power to the furnace was controlled by an
controller (Asahi rika, Japan). Thermocouples were not
side the reactor during the reaction tests because the
erial could exhibit catalytic behavior for hydrocarbon
ion [14]. Instead, the temperature distribution inside
along the flow direction and the temperature of the
k bed under transient and steady states were measured
nert gas flow condition prior to the reaction tests. In